By now, probably most of you have read that NASA selected Gale Crater as the target for the Mars Science Laboratory that will land there next summer. Many news accounts repeated the story that all four landing site finalists would have made great sites, and that the science community wasn't able to come to a consensus about which one was a priority.

The journal Science has just published an article that gives the back story on the ultimate selection process. Unfortunately, a subscription is required, so anyone without a university library account is unlikely to be able to read the piece. So, I'll give a quick summary of the key points.

Gale Crater stands out for its geomorphic and compositional diversity. Unfortunately, no one knows how that big mountain in Gale Crater with all its layers formed. Wind blown dust? Volcanic ash? Impact debris? Science titled its story, "How an alluring geological enigma won the Mars rover sweepstakes." That term, enigma, Science reports, comes up a lot in discussions about Gale.

So, why did an enigma win? Here's what Science reports:

Mawrth has the most ancient materials (big plus), but as with Gale, no one knows how they formed. Also, the geology of Mawrth has been changed by a nearby impact, and the fear was that scientists wouldn't be able to tease out its history. As an additional problem, this site lacks geological diversity, and driving there might be like driving across the surface of Meridiani Planum, the Opportunity rover's site. (Fortunately, Opportunity has had craters to explore, but there's not a whole of diversity in between.)

Holden Crater lacks a delta to indicate that it ever had a lake, and the MSL mission is all about exploring sites modified by water.

Eberswalde Crater has a delta and eventually became the runner up site. While the layers in the delta would make an enticing target for exploration, this site lacked the diversity of Gale Crater.

In the end, the diversity of Gale Crater plus its abundance of water-altered strata won the day. As a bonus, the smooth plain where the rover will land may be a delta. For a mission of exploration, an enigma with diversity presents an opportunity.

Tuesday, July 26, 2011

This post will conclude a three part series on planning for the Mars 2018 rover mission that began with a look at the political and budgetary context for the mission and then the engineering building blocks available for constructing the mission. With this final post (until we have new news), I'll look at the science goals for the mission. (When I began, I didn't realize this would be a series, so the first entry is unnumbered.)

As with so much of this mission, the goals began as two separate set of goals. ESA looked to extend the science that the Mars Science Laboratory (MSL) will begin next year -- in-depth analysis of samples on the surface of Mars. The ExoMars rover has a larger suite of instruments than MSL, and unlike MSL which will collect its samples near the surface, MSL would drill up to two meters below the surface. NASA's rover, by contrast, would focus on collecting and caching samples from within a few centimeters of the surface. If the samples were eventually returned (requiring two follow on missions), the full sophistication of instruments on Earth would be used to unveil the secrets of the Red Planet

Now that ESA and NASA have decided to pool their resources to fly a joint 2018 rover, a science working group has begun defining the goals for the combined mission. The group shared it's early thinking at a joint European and American Mars Exploratory Analysis Group (MEPAG) meeting last month.

A number of presentations discussed the goals and implementation of the merged rover, with the focus of the discussion on the sample collection goals. This may reflect the relative maturity of the previous rover concepts. While NASA's rover was in early definition, the ExoMars rover was ready to cut metal and proceed towards launch prior to the merger of the two programs. However, what unites these two missions (other than the need to pool financial resources) is their goal to, "Search for evidence of past and present life on Mars."

Mars may or may not prove to have signs of life (at least at the spots we explore), but it is unique in at least one respect. It retains a record of conditions on a world with a significant atmosphere and liquid water from when it and the solar system was young. While the first and mandatory goal is to search for signs of life or habitability, five mission goals focus on understanding the early formation of Earth-like worlds and the processes acting on their surface, especially those involving water. (Two goals relate to evaluating Mars for potential human exploration.)

The science goals lead to a list of required samples to cache. Highest priority goes to samples that have been exposed to water in the earliest epochs of Mars to look for signs of life and to better understand the role liquid water played in that planet's history. The next goal is to sample igneous rocks to determine the process of early planet formation. Rounding out the requirements would be samples of regolith (the dust, sand, and gravel on the surface) and the atmosphere.

The atmosphere can be sampled from any location, and regolith will be present almost anywhere. Studies from orbiters have revealed many locations altered by water and many with volcanic rocks. An early assessment of potential landing sites is showing that finding ancient water-altered material and volcanic rocks at the same site may prove difficult within reasonable roving distances. ESA and NASA plan to follow the same open process used to select the Mars Science Laboratory's landing site, and the science community has five to six years to find one or more sites that possess the right surface materials.

Editorial Thoughts: I am a strong supporter of the 2018 merged rover mission. Even if samples are never returned to Earth, the mission will continue the work of sophisticated analysis of samples at Mars that will begin next year with the landing of the Mars Science Laboratory (MSL). Presumably, this rover will go to a second site, but if MSL finds strong signs of possible life, it may follow up MSL's discoveries at Gale Crater. The investment of $1-1.5B by each space agency just for this goal seems to me to be a worthwhile investment.

The merged rover also offers the opportunity for a far more robust sample caching mission. NASA's original plan had been to collect samples from near the surface, where multiple forces can destroy organic material. ESA's deep drill offers the opportunity to collect samples from depths where more pristine samples are likely. There will have to be some engineering work done to enable the transfer from ESA's drill to NASA's sample cache system, so this is not a done deal, but it is a great opportunity.

Beyond the immediate great science that can be done on the surface of Mars by the rover, there is the hope that with samples collected and waiting on Mars, that governments will pony up the further investments needed to return those samples to Earth.

This mission still may face significant budgetary challenges -- it is a Flagship-scale mission in an era where budgets are tight on both sides of the Atlantic. I have my fingers crossed.

Sunday, July 17, 2011

Sometime over the past twenty-four hours, this blog received its 100,000th visit. This probably vastly understates the actual number of posts read since many people use news readers to keep up with blogs. (I know that I do.)

Still, it is a nice milestone. This is a specialized blog that appeals to people not only interested in planetary exploration, but also interested in the twists and turns that missions follow from concept to launch.

Thanks to all of your for taking your time to read what I write; I do appreciate it.

Thursday, July 14, 2011

There's a new plan in the works to enable missions to Europa that bears a resemblance to a proposal first put forward in a European study and to a proposal put forward in a Decadal Survey White Paper.

Europa has proven to be such a hostile world to explore that it has wrecked a flotilla of proposed missions before any were approved for development. My library contains papers and reports on a dedicated mission to explore this moon and its ocean that date back at least fifteen years. Any mission is challenging -- deliver a spacecraft with a battery of high data rate instruments deep into Jupiter's gravity well and survive harsh radiation for weeks or months. Estimates of mission costs have run from ~$1B (a challenge goal, not met) to a behemoth that would have dwarfed any mission ever launched to the planets. The most recent was the Jupiter Europa Orbiter (JEO) that would have flown a highly capable spacecraft to orbit that moon for the better part of a year. Unfortunately, the estimated $4.7B price tag was politically unfeasible.

In an abstract ("A Pragmatic Path to Investigating Europa’s Habitability") for the upcoming (October) EPSC-DPS Conference, we are getting our first look at what a revised Europa program may look at. While the abstract is brief -- likely reflecting the limited time that has been available for analysis -- it's clear that a radical restructuring of the mission is being proposed. This work in progress comes from a NASA-chartered Europa Science Definition Team (ESDT). At the conference, they will "will report on the status of this evolving concept, and will solicit community feedback."

The mission they are considering would split the goals for Europa studies between two spacecraft. One would orbit Europa with a "very small" geophysics payload to perform those measurements that can "best carried out from Europa orbit." A second spacecraft would orbit Jupiter and carry out imaging and other remote sensing during multiple flybys. The abstract authors note that this minimizes the capabilities required by the Europa orbiter, lowering costs related to radiation hardening. The multi-flyby spacecraft would need far less radiation hardening, and would have substantial time between flybys to relay the large volumes of data that would be collected by the imaging and spectral instruments. The two spacecraft would be "phased in time", suggesting that they would be launched separately, perhaps years apart.

Editorial Thoughts: This new mission concept resembles the two spacecraft concept proposed by a European study. In that proposal, a small spacecraft would orbit Europa and use a second Jupiter-orbiting spacecraft to relay the Europa data and conduct independent Jovian studies. This approach both minimized the size of the spacecraft that needed to be hardened to withstand the radiation at Europa, and reduced the power and communications capabilities required by that spacecraft. While discussions about Europa missions often focus on the radiation (literally lethal to electronics), providing the power and communications systems to relay gigabytes of data in near real time during the short orbital life is equally a cost driver. Putting the high data rate instruments on a flyby spacecraft reduces the power and communications requirements because the data from each flyby can be sent in the days to weeks between encounters.

A Decadal Survey White Paper authored by David E. Smith of the Goddard Spaceflight Center also proposed splitting the JEO goals among multiple smaller orbiters. His proposal did not include a multi-flyby spacecraft for remote sensing.

While the abstract doesn't discuss which instruments would be on which spacecraft, I'll hazard some guesses based on the requirements set forth by the JEO science team:

Europa Orbiter

Laser altimeter to measure tides in the icy-surface

Ice penetrating radar to measure ice depth and look for liquid pockets within the ice

Radio science to measure mass distributions within Europa

Magnetometer to study magnetic fields induced by the ocean

Multi-flyby Spacecraft

Multi-color cameras

Visible-Infrared imaging spectrometers to measure surface composition

The idea of a multi-flyby spacecraft suggests some interesting possibilities. If ESA selects the Ganymede orbiter as its next large science mission, it could be tasked with the remote sensing flybys. The proposed mission already calls for a number of flybys of Callisto before orbiting Ganymede. A mission architect who has looked at Jovian moon missions has told me that it would not be difficult to add the additional radiation hardening needed to enable a number of Europa flybys.

If ESA doesn't select its Ganymede mission proposal, then NASA may revive its own similar proposal. Or the multi-flyby spacecraft could be kept as a Jupiter orbiter and used first for an Europa campaign and then for Ganymede and Callisto flyby campaigns. (Io flybys would require additional radiation hardening that might drive costs too high, although flybys at the end of mission might be conceivable.)

It will be interesting to see which mission the ESDT recommends for flight first. The Europa orbiter would return unique measurements that don't duplicate the limited data previously returned by the Galileo mission. On the other hand, the multi-flyby spacecraft would enrich our understanding of Europa and allow better planning for an orbital mission. It's also possible that the orbital mission might carry a camera for higher resolution, stereo imaging a few high priority sites identified by the multi-flyby spacecraft.

NASA will not be in a position to decide on its own mission(s) for at least a year or two at best. In the meantime, ESA will decide on its Ganymede orbiter, and NASA can make its decision in light of ESA's plans. There is no reason why the Europa orbiter could not be an international mission with contributions from two or more space agencies. Budgets are tight everywhere, and pooling resources makes sense.

Wednesday, July 6, 2011

The candidates landing sites for the Curiosity Mars Science Laboratory have been winnowed to two: Gale Crater and Eberswalde Crater. Space.com is one of many sites carrying this news. Editorial Thought: Alas, my favorite, Mawrth is out of the running, apparently because the geology of the site was too difficult to figure out. The two remaining sites, however, are both exciting locations, and I look forward to learning about one of them in depth.

In the first step towards enacting the FY12 NASA budget into law, the House has proposed a a bit less than a 10% cut to NASA's science program, including cancelling the James Web Space Telescope. Science.com is one of many sites summarizing this news. Editorial Thought: This is one of many steps in the dance that eventually results in final ratification of NASA's budget for next year. While this second step (the President's budget proposal was the first step and was largely good news for the science program) has bad news, there is still the Senate's take on the budget to come. And looming over the dance are the overall discussions to cut the growth in the budget substantially. Ultimately, the news for the science program may be neutral to bad (I don't see a scenario where the budget increases over the President's proposal), but we are unlikely to know the ultimate resolution for some time.

The journal Nature has an article on the shortage of senior scientists with experience as mission Principal Investigators for the next round of Discovery mission proposals. Editorial Thought: Most interesting to me was the statement that each Discovery proposal led to "proposals 'from the same guys'." This echoes statements from an abstract at the recent Low Cost Planetary Mission conference, "...as is the case with many regularly offered competitions, proposers often find that they must propose multiple times, improving their mission concepts based on review results and additional study, before a mission concept achieves sufficient quality for selection. This presents NASA with more mature, higher quality mission concepts from which to choose. However, over time, it can also stagnate the pool of proposed mission concepts as the selection pool NASA faces becomes filled with only those proposals that are continually resubmitted and strengthened. Diversity can suffer, and instead of a selection process in which the best, most exciting concepts rise to the top, instead an assembly line of steadily maturing mission concepts waiting their turn for selection is produced." (Opening up the Box: ASRG Missions in the Discovery Program, Curt Niebur). (NASA has at least partially broken this cycle by allowing ASRG plutonium power sources for at least the current Discovery competition.)

Tuesday, July 5, 2011

Last week, I summarized the challenges facing ESA and NASA’s managers as they build the political and budgetary framework for their joint program of Mars exploration.In the meantime, scientists and engineers from both sides of the Atlantic have been defining the goals and exploring the implementation of the 2018 rover.Two weeks ago, a number of them met in the first international Mars Exploration Analysis Group (MEPAG) meeting to discuss those plans among other topics.Only brief mention in the presentation material was made to the budget by noting that, “The 2018 [rover] mission is very cost constrained.”

While it appears that the definition of the science goals is well advanced, the engineering analysis is in the early stages.As a result, the presentations in the meeting and their summary here are status reports for an on-going process.Details can and probably will change.

Previous objectives of the separate 2018 rovers

Until a few months ago, the 2018 mission was to be two rovers, delivered by a single lander, that would separately explore the same area.ESA’s rover would drill beneath the surface, hoping to find pristine samples to analyze with a sophisticated laboratory.NASA’s rover would examine materials at the surface with a less sophisticated set of instruments on a robotic arm and collect and cache a small number of them for possible return to Earth by future missions.While there were opportunities for collaborative exploration, each rover had distinct goals.

Budget realities for both space agencies have forced the decision to fly a single rover that will combine the goals of both agencies.Today, I’ll look at the scientific building blocks – the instruments – available to the combined mission.In the next post, I’ll discuss how scientists plan to make use of what would be the most sophisticated set of capabilities ever landed on another world.

To understand the challenges faced by the engineering teams, it helps to begin with some background on the types of measurements that can be done by a Mars surface mission:

Remote sensing instruments image the surroundings and use spectrometers to remotely characterize composition of surface materials.While providing important measurements in their own right, these instruments also allow scientists to select targets for in-depth measurements with other instruments or for possible return to Earth.The MER rovers had cameras and a thermal emission spectrometer; the MSL lander will have cameras and the ChemCam instrument that uses a laser to vaporize materials for spectral measurements.ESA’s ExoMars rover would have had cameras, an infrared spectrometer, and a ground penetrating radar as remote sensing measurements.Many images and measurements can be made in a day.

Contact instruments place are placed against the surface material to be measured.The MER rovers carried two contact spectrometers and a microscopic imager, while MSL would carry a single contact spectrometer and a microscopic imager.These instruments enable fairly rapid measurements (1-3 days per target) and the measurements can be repeated at as many targets as time permits.

Analytical laboratory instruments require samples to be brought inside the rover or lander but provide more sensitive measurements than the contact instruments.The sample material can also be manipulated in ways – such as wetting to induce chemical reactions or heating to vaporize materials – that are impossible with contact instruments.The downside to these instruments is that sample acquisition and measurements take longer (10-20 days), and some of the instruments have a limited number of experiment chambers.As a result, these instruments allow in-depth analysis of a fairly small number of samples.The MER rovers had no instruments in this category, the Phoenix lander had several analytical instruments within two instrument suites, the MSL lander will have two suites of analytical instruments, and the ExoMars rover would have had five suites.

(For simplicity, I have not included all instruments from each mission in the summary above.)

New goals for the single joint rover

The fundamental challenge for merging the rover missions previously planned by each space agency will be to accommodate their different suites of instruments.Both rover missions would have had remote sensing instruments.However, NASA’s MAX-C rover would have relied entirely on contact instruments and a surface drill located on an arm for its analysis and collection of surface materials, a strategy driven by that mission’s need to rapidly assess a number of potential materials to select the very few that would be collected for sample return.ESA’s Exo-Mars rover, on the other hand, would have forgone surface contact instruments to focus on a highly capable analytical laboratory suite.This mission would also have acquired samples only through a drill that could return material from as deep as two meters below the surface.(The goal is retrieve more pristine samples that have not been altered by the harsh conditions at and near the surface.)

The new rover retains the ExoMars goal to analyze samples collected

from depths below agents that are likely to destroy organic materials

The current vision for the new single rover would have it retain all the capabilities of NASA and ESA's rovers in a single rover.

The simplest implementation of the joint 2018 rover would keep the MAX-C and ExoMars heritage instruments distinct.In this option, samples for possible return are analyzed and collected by the rover’s arm and a surface sampling drill.Samples collected by the ESA deep drill could be analyzed only by ESA’s analytical instruments (and two ‘contact’ instruments that examine material along the bore hole).A potentially interesting surface sample foundby the arm instruments could not be passed to the analytical instruments for a second opinion.Similarly, a really interesting sample brought up by the deep drill could not be passed to the arm to add to the sample cache for eventual return to Earth.

The science teams setting the goals for the joint rover recognized these limitations.Their members have assigned a very high priority to allowing samples collected by the deep drill for inclusion in the return cache.The ability to pass samples from the arm’s near surface drill to the analytical laboratory for analysis also would be valuable, but would be a lower priority.

Unfortunately, adding these requirements to trade samples between the surface and deep drill elements of the rover requires redesigns.For example, ESA’s analytical laboratory instruments have been largely designed.Moving them and the deep drill to a location in the rover where they could interact with the arm and sample cache hardware would require a redesign (degree of difficulty not discussed in the presentations).

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.